Sick CDTV: black screen, but runs programs

[fiat1100d]

Hello to everybody! Many wishes of an happy 2010! :-)

Unfortunately the last days of the 2009 made my CDTV sick: it doesn't display screens anymore, both via RGB or composite (from the genlock) output. It does run software on CDs and on floppy disk, e.g. I can hear the typical sounds from the drive made by Workbench while loading.

Has anyone got an idea? I tried to replace Denise, but got no luck. I think Agnus does manage memory too so I hope it is not the sick component, being an 8375 on a MegAChip.
Can someone point me to a good troubleshooting guide?

Thanks!
Daniele

[fiat1100d]

Hi,
you have a fried fuse.
It's usually looking like a green resistor

It seems there aren't fuses near the video output, but I found another forum (http://eab.abime.net/showthread.php?p=610700) where they say it probably is the video hybrid chip.

[fiat1100d]

I think I saw that kind of part (green fuse) on some A500 but I haven't located it on the CDTV.

However, I replaced the hybrid and problem is still there, but there is some news.
It seems that, with a fully "discharged" CDTV (that is, having it disconnected from mains power for hours), after powering it on the the video output is displayed but goes away after some seconds.

So, starting from "discharged" unit:
- turn on monitor (for having it ready to display);
- connect CDTV to mains power and turn on;
- regular CDTV display for a while;
- colour goes away;
- no display.

Any idea?
I think it could be really related to some capacitor, because for displaying the CDTV needs to be disconnected from mains for a while and this should discharge the capacitors.

Thanks!

[fiat1100d]

Finally, after replacing:
- video hybrid, with a 390229-03 (from A500+)

- two big 3300uF capacitors near video hybrid
- a leaked capacitor on the genlock module

here is what I can see:
- correct colour display on 23 pin RGB port (was no video at all initially)
- B/W display with original video module (both composite and RF output)
- B/W display using composite output of genlock module

Where the problem could be now? :-?
Composite and RF should be generated on the modules using RGB signals as far as I know, could then be some broken circuit trace?

• I do believe that, probably, the hybrid was fine and the issue was with the capacitors... unfortunately I destroyed the original hybrid when desoldering :-(